Technical Field
This disclosure relates to precision metrology, and more particularly to adjustable magnification optical systems such as machine vision inspection systems.
Description of the Related Art
Adjustable magnification optical systems may be utilized in precision non-contact metrology systems such as precision machine vision inspection systems (or “vision systems” for short). Such vision systems may be utilized to obtain precise dimensional measurements of objects and to inspect various other object characteristics, and may include a computer, a camera and optical system, and a precision stage that moves to allow workpiece traversal and inspection. One exemplary prior art system, characterized as a general-purpose “off-line” precision vision system, is the QUICK VISION® series of PC-based vision systems and QVPAK® software available from Mitutoyo America Corporation (MAC), located in Aurora, Ill. The features and operation of the QUICK VISION® series of vision systems and the QVPAK® software are generally described, for example, in the QVPAK 3D CNC Vision Measuring Machine User's Guide, published January 2003, and the QVPAK 3D CNC Vision Measuring Machine Operation Guide, published September 1996, each of which is hereby incorporated by reference in its entirety. This type of system uses a microscope-type optical system and moves the stage so as to provide inspection images of either small or relatively large workpieces at various magnifications.
General-purpose precision machine vision inspection systems are generally programmable to provide automated video inspection. Such systems typically include GUI features and predefined image analysis “video tools” such that operation and programming can be performed by “non-expert” operators. For example, U.S. Pat. No. 6,542,180, which is incorporated herein by reference in its entirety, teaches a vision system that uses automated video inspection including the use of various video tools.
In various applications, it is desirable to perform high speed autofocus and/or other operations to facilitate high-speed measurements for high throughput in either stationary or non-stop moving inspection systems. The speed of autofocus and other operations requiring focusing in conventional machine vision inspection systems is limited by the motion of the camera through a range of Z-height positions. There is a need for improved autofocus and/or other operations utilizing alternative methods of collecting images of a range of focus distances (e.g., stacks of images for measuring Z-height positions) at a high speed and which particularly are operable at different levels of magnification without compromising the range of focus, image quality and/or dimensional accuracy in the images.